Roofing shingles are comprised of a headlap portion and a butt portion; granules are often used in both of such portions. Reference may be had, e.g., to U.S. Pat. No. 3,921,358 (a composite asphalt-impregnated felt roofing shingle comprising a rectangular sheet having a headlap portion and a butt portion), U.S. Pat. No. 4,717,614 (a shingle whose headlap portion is coated with a layer of asphaltic material), U.S. Pat. No. 4,900,589 (a process for applying granules to a moving sheet having a headlap area and a butt area for making a shingle roofing product), U.S. Pat. No. 6,358,305 (a process of preparing a darkened headlap for a roofing shingle), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
U.S. Pat. No. 6,358,305 of Ingo B. Joedicke discloses coated headlap granules that may comprise “ . . . limestone, rock, greenstone, nephylene syenite, gravel, slate, ganister, quartzite, and greystone . . . ” granules (see lines 30-34 of column 4). The patent discloses “The granules are typically in a size range between about 10 to 35 mesh, i.e. particle sizes which will pass through an 8 mesh screen but retained on a 35 mesh screen . . . ” (see lines 34-37 of column 4).
In the Examples of U.S. Pat. No. 6,358,305, an experiment is described in which “ . . . dedusted headlap-grade crushed rock aggregate . . . ” was used. However, Joedicke discloses that the aggregate may also be made from “ . . . limestone, . . . greenstone, nephylene syenite, gravel slate, ganister, quartzite, and greystone . . . ” (see lines 30 to 34 of column 4 of such patent); but he does not disclose, e.g., how one would prepare a “dedusted, headlap-grade” limestone material.
When a headlap material is made from limestone using the process disclosed in the Joedicke patent, the adhesion properties the headlap granules so produced are not satisfactory.
It is an object of this invention to provide a headlap material comprised of at least 95 weight percent of calcium carbonate that has acceptable adhesion properties.
It is another object of this invention to provide a bituminous roofing product with acceptable properties that is comprised of headlap granules that contain at least about 95 weight percent of calcium carbonate.